Antenna system

ABSTRACT

A multi-channel microwave antenna system having a plurality of antennas and adaptable for use with aerodynamic or space vehicles. The system is of small size and light weight and has good decoupling between channel antennas. Dielectric radiators are embedded in a foam dielectric in an end fire array in the ends of four rectangular waveguides. Each pair of waveguides forms the transmitting and receiving portion of a separate antenna system. The receiver arm of one system and the transmitter arm of the second system are coupled and matched to their respective radiating elements, through a two step twist section of waveguide which changes the polarization to match that of the adjacent channel. Each transmitter and receiver waveguide pair is coupled to a balanced mixer in the form of a magic tee.

nited States Patent 1191 Jones, Jr.

[ l ANTENNA SYSTEM [75] Inventor: Howard S. Jones, Jr., Washington,

, [73] Assignee: The United States of America as represented by the Secretary of the Army, Washington, DC.

22 Filed: May 18, 1966 211 App]. No.: 552,376

[56] References Cited UNITED STATES PATENTS 2,419,205 4/1947 Feldman 343/785 X 3,268,902 8/1966 Turrin 343/785 X [451 Dec. 311, 1974 Primary ExaminerT. H. Tubbesing Attorney, Agent, or FirmSaul Elbaum 57 ABSTRACT A multi-channel microwave antenna system having a plurality of antennas and adaptable for use with aerodynamic or space vehicles. The system is of small size and light weight and has good decoupling between channel antennas. Dielectric radiators are embedded in a foam dielectric in an end fire array in the ends of four rectangular waveguides. Each pair of waveguides forms the transmitting and receiving portion of a separate antenna system. The receiver arm of one system and the transmitter arm of the second system are coupled and matched to their respective radiating elements, through a two step twist section of waveguide which changes the polarization to match that of the adjacent channel. Each transmitter and receiver waveguide pair is coupled to a balanced mixer in the form of a magic tee.

8 Claims, 10 Drawing Figures PMENTEDBEE3 1 1914 I 3,858.2l4

INVENTOR Howard 5. M52266, Jr.

$ m ATTORNEYS 1 ANTENNA SYSTEM This invention relates to an antenna system and more particularly to a system utilizing dielectric rod radiators evidencing improved performance, decreased size and weight, and good isolation between operating channels. In the preferred embodiment, the antenna system forms part of a dual fuse microwave system, with each fuse utilizing two dielectric rod radiators combined with a unique microwave mixing network.

In the design of fuse and radar systems, it is often necessary to have an antenna system that produces a beam of energy directed along the missile axis. Two conventional methods commonly employed for this purpose involve the use of electromagnetic horns and parabolic antennas. However, in cases where separate transmitter and receiver antennasare required, the use of horns and other techniques poses unusually difficult design problems. For example, the physical size and configuration of horns are generally incompatible with the overall system design for the beam widths that are required. Also high'isolation between antennas is difficult to obtain utilizing these methods. A third method,

employing slotted wave guide antennas, requires excess space and weight, as well as complex feed lines.

The present invention avoids the above-mentioned difficulties by providing an antenna system incorporating dielectric rod radiators. In the preferred embodiment, these radiators are incorporated in a dual homodyne microwave fuse system. Eachsystem consists of a balanced wave guide mixer network, which is coupled to both a transmitting and receiving antenna, each in the form of a dielectric rod radiator. The entire assembly is mounted compactly on a seven inch diameter plate with the antenna system on one side and the balanced mixers on the other.

The directional properties of dielectric rod radiators are extremely useful at the UHF and microwave frequencies required in fusing applications. When properly excited they produce a single lobe of radiated energy with its maximum directed along the axis of the rod. The directivity of this end fire radiation is proportional to the length of the rod. Electromagnetic waves propagated along the axis of these cylindrical rods are excited in theHE (asymmetric) hybrid mode which has no cut off frequency. Data compiled on decoupling between dielectric rod antennas as a function of frequency for various transmitter and receiver channels indicates that decoupling varies from 27 to 50 db in the frequency range of from 9.0 to ll gc. Values ranging from 30 to 50 db are obtainable from 9.7 to l l gc, i.e., the transmitter and receiver of each system are separated from each other by 30 db or more over a percent bandwidth and one system is isolated from the other by the same magnitude..For certain channel combinations, the decoupling is in excess of 40 db throughout a percent frequency hand. These measurements are far better than would be expected from the use of other antenna design methods for fuse systems requiring end fire radiation. Also the results are at least equivalent to or in some instances better than those of broadside arrays where the physical separation of antennas is far greater.

In addition to good directivity and isolation between channels, an important feature of the present invention resides in the provision of a multi-channel system having a plurality of antennas which effectively conserves and utilizes the limited weight and space available in an aerodynamic or space vehicle such as a missile or the like. In the present invention, a dual microwave system is incorporated in the space normally reserved for a single system. Other notable improvements provided by this invention are its ready adaptability to other parts of conventional microwave systems, high decoupling between radiators, good performance over a wide frequency range, high gain and narrow beam widths.

It is therefore one object of the present invention to provide an improved antenna system.

Another object of the present invention is to provide an improved antenna system incorporating a plurality of dielectric rod radiators.

Another object of the present invention is to provide a compact dual microwave fuse antenna system.

Another object of the present invention is to provide a four channel microwave antenna system of small'size and light weight having good decoupling between channel antennas. In the dual fuse system, dielectric (ceramic) radiators are locked by a plastic foam dielectric or other suitable material in an end fire array in the ends of four rectangular wave guides. Each pair of wave guides forms the transmitting and receiving portion of a separate antenna system for a dual fuse assembly. The receiver arm of one system and the transmitter arm of the second system are coupled and matched to their respective radiating elements, through a two step twist section of waveguide which changes the polarization to match that of the adjacent channel. Each transmitter and receiver wave guide pair is coupled to a balanced mixer in the form of a magic tee. The transmitter channel is attached to the E-plane arm of the magic tee. Slots cut in a common wall formed by this union provide a coupling path for local oscillator power to drive a pair of mixer crystals that are mounted in the colinear arms of the magic tee. The receiver signal enters the I-I-arm and divides equally to each magic tee crystal, mixing with the local oscillator signal so as to generate an IF output signal. The other end of the E-plane arm is terminated into a very short matched load to prevent reflections.

These and further objects and advantages of the invention will be more apparent upon reference to the following specification, claims and appended drawings, wherein:

FIG. 1 is a perspective view of the nose of a missile with a portion broken away to show the dual fuse antenna system of the present invention;

FIG. 2 is an end view of the four radiators of the antenna system of FIG. 1;

FIG. 3 is a side view with parts broken away showing the construction of one of the dielectric rod radiators of the system of FIG. 1;

FIG. 4 is a plot of the two-way E and I-I-plane radiation patterns of the complete antenna system of FIG. 1; FIG. 5 is a view showing the E-plane antenna system; FIG. 6 is an end view of the E-plane system of FIG.

FIG. 7 is a view showing the I-I-plane antenna system of the present invention;

FIG. 8 is an end view of the I-I-plane system of FIG.

FIG. 9 is a simplified circuit diagram of one of the antenna systems showing its coupling to a balanced mixer; and

FIG. is a perspective view showing the antenna feed and balance mixer structure used with each of the antenna systems of FIGS. 5 and 7.

There are many complex problems involved in the complete understanding of the properties and behavior of RF fields and modes in dielectric media. When properly excited dielectric rods produce a single lobe of radiated energy with its maximum directed along the axis of the rod. The directivity of this end fire radiation is proportioned to the length of the rod. Electromagnetic waves propagated along the axis of the cylindrical rods are excited in the HE, (asymmetric) hybrid mode which has no cut off frequency. The energy concentration and phase velocity of the dielectric are both functions of the rod diameter D and dielectric constant (6). These are very useful properties because as the dielectric constant is increased a smaller rod diameter is required for a given frequency, thus reducing the volume and weight of the radiating element. For small values of D/)\ compared with unity, most of the energy is propagated outside the rod, while for large values of D/)\ energy is concentrated within the rod. For use in the X- band frequency range, it is preferred that the rods be formed of aluminum oxide with a dielectric constant of approximately 9.0 and a loss tangent of 0.002.

Referring to the drawings, FIG. 1 is a perspective view showing the novel antenna system of the present invention generally indicated at 10, incorporated in the nose 12 of a missile 14. The system comprises four aluminum oxide dielectric rods 16, 18, and 22 of circular cross section received in the end of respective rectangular wave guides 24, 26, 28 and 30. The ends of the rods are embedded in the wave guides by a suitable polyfoam dielectric formed for example by a polyethylene or polystyrene dielectric foam, as indicated at 32. Wave guides 24 and 26, which form a portion of the E- plane antenna assembly of a dual fuse system are mounted on a 7-inch diameter plate 34 and are coupled to a balanced mixer generally indicated in FIG. 1 at 36. The H-plane wave guides 28 and 30 are similarly mounted on base plate 34 and are coupled to a second similar balanced mixer 38, which along with mixer 36 is attached to the other side of plate 34.

FIG. 2 shows the relationship in an end view of the radiators and wave guides with respect to mounting plate 34. Radiating rods 16 and 20 are aligned along a horizontal plane 40 in FIG. 2 while radiators 18 and 22 are similarly aligned along a parallel plane 42. Wave guides 24 and 26 and hence the radiators 16 and 18, which are centered along the longitudinal axis of the wave guides, are offset such that the adjacent broadsides of the wave guides 24 and '26 lie substantially in a common vertical plane. The position of the H-plane wave guides 28 and 30 which support rods 20 and 22 along their longitudinal axis is determined by the desired spacing between the respective E-plane and H- plane antenna systems. The distance between the longitudinal axes of rods 16 and 20 is preferably the same as the distance between the longitudinal axes of rods 18 and 22, and both of these distances are preferably selected as at least approximately equal to the distance between the parallel planes 40 and 42. As an example, this distance in one embodiment constructed in accordance with the present invention was 1% inches for X- band radiation. However, center-to-center spacings ranging from 6 inch to 4% inches between two adjacent parallel rods may be satisfactorily used depending upon rod size, frequency, desired isolation and the like.

FIG. 3 is a side view with portions broken away showing the support arrangement for one of the dielectric rods in its supporting wave guide. By way of example, rod 16 is illustrated in FIG. 3 as supported in E-plane wave guide 24, it being understood that the other rods and wave guides are similarly constructed. Wave guide 24 is provided with a mounting flange 44 and is partially filled with foam dielectric 32 to receive and rigidly support the short tapered end 46 of rod 16. In addition to short tapered end 46, the rod 16 includes a straight cylindrical section 48 of uniform diameter joined to a longer truncated conical section 50 of more gradual taper to its blunt tip 52. In one embodiment constructed in accordance with the present invention,

the dielectric rod 16 had an overall length of 6 inches, with the sharply tapering section 46 extending for a distance of 1 inch, the constant diameter section 48 having a length of 2 inches, and the truncated conical section 50 tapering over the remaining three inches of the aluminum oxide (ceramic) dielectric rod. Rod 16 projected outwardly from the end 54 of the wave guide a distance of 3% inches. The diameter of larger section 48 was 0.290 inch, which tapered to a blunt tip 52 having a diameter of 0.150 inch.

FIG. 4 is a plot of the two-way E and I-I-plane radiation patterns of the complete antenna system 10 of FIG. 1, when positioned in air outside of the missile nose. The H-plane pattern is indicated by dashed lines 58 and the E-plane antenna system pattern is indicated by the solid line 60 in FIG. 4. When incorporated in a missile nose, the surrounding dielectric material, surrounding radome structure, or the like may slightly modify the radiation pattern from that illustrated in FIG. 4, but this can be readily compensated by suitable choice of materials and in any event produces no serious adverse effect.

FIGS. 5 and 6 show the single E-plane system incorporating just the two dielectric rods 16 and 18. These rods are supported in wave guides 24 and 26, the wave guide 24 passing through the mounting plate 34 and terminating in the flange 62 adapted to be coupled to a microwave transmitter. Thus, wave guide 24 constitutes a transmitter channel for passing microwave energy from a suitable transmitter to radiating rod 16 from which energy is radiated into space. The other wave guide 26 of the E-plane configuration of FIGS. 5 and 6 is connected through a double step twist section of wave guide 64 which rotates 90 degress the polarization of energy initially impinging upon E-plane receiving antenna rod 18. The rotated polarization energy passes through a short section of wave guide 66 to the balanced mixer 36 in a manner'more fully described below.

FIGS. 7 and 8 show the I-I-plane configuration which may be used separately by itself (as can the E-plane system of FIGS. 5 and 6) or in conjunction with the E- plane configuration of FIGS. 5 and 6, the combination assembly forming the preferred embodiment and illustrated in FIGS. 1 and 2. In FIGS. 7 and 8, receiving rod 20 and receiving I-I-plane wave guide 28 are coupled to the balanced mixer 38. Transmitting rod 22 and H- plane wave guide section 30 are connected through a similar double step 90 twist section of wave guide 68 to rectangular wave guide 70 which also passes through plate 34 and is provided with a flange 72 for connection to a second microwave transmittter (or to the same transmitter in some instances).

FIG. 9 is a circuit diagram illustrating the connection of the antenna rods 16 and 18 to the balanced mixer 36 which is constructed in the form of a magic tee. It is understood that balanced mixer 38 is of similar construction, only mixer 36 being illustrated for the sake of simplicity. The physical construction of the balanced mixer is illustrated in FIG. 10.

Referring to FIGS. 9 and 10, the E-plane transmitter wave guide 24 is connected to a transmitter source 74 for producing microwave energy in the X-band frequencies. By way of example only, source 74 may take the form of a klystron coupled by an appropriate lead 76 such as a coaxial cable or the like to wave guide 24. Also coupled to wave guide 24 is a magic tee generally indicated at 80 having side arms 82 and 84, E-plane arm 86 and an H-plane arm 88. H-plane arm 88 is adapted to receive a microwave input from E-plane receiving rod 18 by way of wave guide 26, 90 twist 64, and wave guide section 66. This input from the receiving antenna is illustrated at 90 in FIG. 10. Side arms 82 and 84 terminate in conventional mixing crystals 92 and 94 which develop an output to the receiver by way of suitable leads 96 and 98 such as coaxial cables or the like.

E-plane arm 86 is quite short and is terminated in a matched load 100. Intermediate this load and the junction of the magic tee, one broadside of arm 86 is connected to or is common with a broadside of the transmitter wave guide 24. Energy is coupled from the transmitter wave guide 24 into the E- plane arm 86 of the magic tee by way of a pair of elongated eliptical slots illustrated by dashed lines at 102 and 104 in FIG. 10, which slots establish microwave communication between transmitter wave guide section 24 and E-plane arm 86 of the magic tee.

In operation, microwave energy from the source 74 passing through transmitter wave guide section 24 is radiated by E-plane rod 16. At the same time, a portion of the transmitter energy is coupled through slots 102 and 104 to the E-plane arm 86 of the magic tee 80, this energy passing downwardly to the junction of the magic tee and through the junction to the crystals 92 and 94 in a well known manner. Any energy from the transmitter through the slots 102 and 104 which passes upwardly of the E-plane arm 86 is prevented from reflecting by the matched load 100 terminating this arm. Energy from the receiving rod 18 passes through the H- plane arm 88 of the magic tee and in a well known manner is divided and passes equally to the matched crystals 92 and 94. The crystals form crystal detectors such that the combination of the transmitter energy from E- plane arm 86 and the received energy from the receiver by way of H-plane arm 88 are mixed in the crystals to produce an intermediate frequency or IF output which may be supplied to a suitable receiver by way of leads 96 and 98.

It is apparent from the above that the present invention provides an improved antenna construction particularly suited for UHF and microwave operation. Important features of the present invention include the improved decoupling between channels along with the small size and light weight of the antenna system so that it may be incorporated in a missile or other device where size and weight are a problem. The two-way radiation patterns taken with the rods are the same for both the E-plane and I-l-plane systems. The two-way gain is approximately 26.5 db, which is what would be expected normally since the one-way gain is approximately 13.5 db and the antennas are similar and looking in the same direction. The side lobe level is suppressed below 30 db in all regions of the pattern spectrum.

The overall size and length of the rods as well as the materials chosen can be varied within wide. limits in accordance with the particular application and operating frequency. Rods have been constructed with radiating lengths (projecting from the wave guide end) of from 3.5 to 4.5 inches. The particular size and spacing should be chosen in accordance with the desired isolation between transmitter and receiver within each system as well as to maintain the best possible decoupling in each channel with respect to all others. The arrangement illustrated in the preferred embodiment of this in vention as shown in FIGS. 1 and 2 for a four channel system constitutes an excellent compromise between good decoupling and the best mechanical lay-out con sistent with the use of other conventional microwave components. In each case, the rods illustrated are excited from a standard X-band (0.4 by 0.9 inch inner dimension) rectangular wave guide operating in its dominant TE mode. Each rod is matched to the wave guide impedance by the smooth tapered transition at its input end as illustrated at 46 in FIG. 3. The beam width, gain, side lobe level of radiated energy and so on can be controlled in several ways. The diameter of the rod has a decided influence on beam width, voltage standing wave ratio, and side lobe level. The tapered transition 50 on the radiating end of the rod provides substantial improvement in pattern characteristics and reduces appreciably the side lobe amplitudes. The rod length to some degree controls the gain and bandwidth, while the dielectric constant determines the wave length and energy concentration in the rod. While the overall length of the rods in the example given is six inches,'others can be varied as desired. Experiments have been made on rods with maximum diameters varying from 0.270 to 0.300 inch. The range of these diameters was limited by the narrow dimension of the wave guide and the smallest diameter to effect energy concentration. The optimum input and output impedance matching transtions were determined by the rod diameters.

To summarize, the present invention while useable in conjunction with two or more dielectric rods, in the preferred embodiment is incorporated in a dual fuse or microwave system with each fuse utilizing two dielectric rod radiators combined with a unique microwave mixer network. Results of decoupling measurements indicate that as much as db decoupling is attainable in the X-band with a 1.5 inch rod center-to-center separation while each rod is matched to a voltage standing wave ratio of 1.2 or better over a 10 percent bandwidth. If desired, the entire assembly illustrated in FIG. 1 including the four dielectric rod radiators of the microwave system may be lock foamed in a conically shaped dielectric medium having a dielectric constant close to that of air. That is, the entire nose of the missile illustrated in FIG. 1 may be filled with a rigid dielectric foam material to lock the complete assembly in place. If desired, a dielectric radome can be attached to the missile and matched to the antenna system. Recent developments in the availability of improved organic and glass ceramic foam materials with very low losses and dielectric constant values (e.g., 1.2 or less) make such a radome construction possible. These materials can be used to form a radome structure over the dielectric rod radiators which physically secures the rods in place and cause only small variations in the radiation pattern.

If desired, the entire area from the input aperture to the mounting plate can be filled with aresistive type dielectric material to provide further isolation between the systems (to reduce skin currents). Also, the system of the present invention can be used in a dual frequency band system with many radiating elements of different sizes for performing different functions. Alternatively, a single antenna can be provided for each system, using circulators which gives better isolation and reduction in space. In all cases, the antenna pattern can be changed by changing dielectric rods, such as changing the rod length, dielectric constant, etc.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

1. An antenna system comprising a pair of dielectric rod radiators positioned in parallel end fire array, the center-to-center spacing of said rods being no greater than 4% inches, and a pair of parallel waveguides, said rods being mounted in and projecting from the ends of said waveguides.

2. A system according to claim 1 wherein said rods are secured to said waveguides by a foam dielectric.

3. An antenna system comprising a pair of dielectric rod radiators positioned in parallel end fire array, the center-to-center spacing of said rods being no greater than 4% inches, a balanced mixer in the form of a magic tee, a mixer crystal in each of the side arms of said magic tee, means coupling one of said rod radiators to one of the remaining two arms of said magic tee, a transmitter, means coupling said transmitter to the other of said rod radiators, and means'coupling said transmitter to the other of the remaining two arms of said magic tee.

4. An antenna system comprising four dielectric rod radiators positioned in parallel end fire array, and four parallel waveguides, said rods being mounted in and projecting from the ends of said waveguides and the center-to-center spacing of said rods being no greater than 4% inches.

5. An antenna system according to claim 4 wherein said waveguides are rectangular and are arranged in E- plane and H-plane transmitter-receiver pairs, a balanced mixer for each of said pairs, each balanced mixer comprising a magic tee, a mixer crystal in each of the side arms of said magic tee, means coupling one of the rod radiators of each waveguide pair to one of the remaining two arms of its corresponding magic tee, transmitter means, means coupling said transmitter means to the other rod radiator of each pair, and means coupling said transmitter means to the other of theremaining two arms of each magic tee, a twist section, one of the rod radiators of each pair being coupled to its balanced mixer through a 90 degree twist section of waveguide.

6. An antenna system according to claim 5 mounted in the nose of a missile.

7. An antenna system comprising four dielectric rod radiators positioned in parallel end fire array, said rods being mounted in and projecting from the ends of four parallel waveguides, the center-to-center spacing of said rods being no greater than 4% inches, said waveguides being rectangular, two of said waveguides lying in an H-plane array and two of said waveguides lying in an E-plane array.

8. A system according to claim 7 wherein said E- plane waveguides are centered in a first pair of spaced parallel planes and said H-plane waveguides are centered in a second pair of spaced parallel planes, said first pair of planes each intersecting said second pair of planes at a right angle, each of said E-plane waveguides also being centered in a different one of said second pair of planes. 

1. An antenna system comprising a pair of dielectric rod radiators positioned in parallel end fire arRay, the center-tocenter spacing of said rods being no greater than 4 1/2 inches, and a pair of parallel waveguides, said rods being mounted in and projecting from the ends of said waveguides.
 2. A system according to claim 1 wherein said rods are secured to said waveguides by a foam dielectric.
 3. An antenna system comprising a pair of dielectric rod radiators positioned in parallel end fire array, the center-to-center spacing of said rods being no greater than 4 1/2 inches, a balanced mixer in the form of a magic tee, a mixer crystal in each of the side arms of said magic tee, means coupling one of said rod radiators to one of the remaining two arms of said magic tee, a transmitter, means coupling said transmitter to the other of said rod radiators, and means coupling said transmitter to the other of the remaining two arms of said magic tee.
 4. An antenna system comprising four dielectric rod radiators positioned in parallel end fire array, and four parallel waveguides, said rods being mounted in and projecting from the ends of said waveguides and the center-to-center spacing of said rods being no greater than 4 1/2 inches.
 5. An antenna system according to claim 4 wherein said waveguides are rectangular and are arranged in E-plane and H-plane transmitter-receiver pairs, a balanced mixer for each of said pairs, each balanced mixer comprising a magic tee, a mixer crystal in each of the side arms of said magic tee, means coupling one of the rod radiators of each waveguide pair to one of the remaining two arms of its corresponding magic tee, transmitter means, means coupling said transmitter means to the other rod radiator of each pair, and means coupling said transmitter means to the other of the remaining two arms of each magic tee, a 90* twist section, one of the rod radiators of each pair being coupled to its balanced mixer through a 90 degree twist section of waveguide.
 6. An antenna system according to claim 5 mounted in the nose of a missile.
 7. An antenna system comprising four dielectric rod radiators positioned in parallel end fire array, said rods being mounted in and projecting from the ends of four parallel waveguides, the center-to-center spacing of said rods being no greater than 4 1/2 inches, said waveguides being rectangular, two of said waveguides lying in an H-plane array and two of said waveguides lying in an E-plane array.
 8. A system according to claim 7 wherein said E-plane waveguides are centered in a first pair of spaced parallel planes and said H-plane waveguides are centered in a second pair of spaced parallel planes, said first pair of planes each intersecting said second pair of planes at a right angle, each of said E-plane waveguides also being centered in a different one of said second pair of planes. 